Check valve is to rely on the media itself to automatically open and close the valve, used to prevent the media back to the valve, also known as check valve, check valve, counter valve, and back pressure valve. Check valve is an automatic valve, its main role is to prevent the media back to prevent the pump and drive the motor reversal, and the container media discharge. The check valve can also be used to provide piping where the pressure may rise above the supply of the system pressure. Check valve can be divided into swivel check valve (according to the center of gravity rotation) and lift check valve (along the axis of movement). The role of this type of valve is to allow only the medium to flow in one direction, and to prevent the direction of flow. Usually the valve is automatically working, in a direction of the flow of fluid pressure, the valve flap open; fluid flow in the opposite direction, by the fluid pressure and the valve flap from the valve seat in the valve seat, thus cutting the flow. The check valve belongs to this type of valve, which includes a swivel check valve and a lift check valve. The swivel check valve has a hinge mechanism, and a valve-like valve flap free to rest on the inclined seat surface. In order to ensure that the valve flap reaches the proper position of the valve seat each time, the valve flap is designed in the hinge mechanism so that the flap has sufficient swivel space and the flap is truly and fully accessible to the valve seat. The flap can be made entirely of metal, or it can be embedded in metal, leather, rubber, or synthetic coverage, depending on the performance requirements. Swing check valve in the fully open condition, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The flap of the lift check valve is located on the valve seat sealing surface of the valve body. This valve in addition to the valve can be free to lift, the rest as the same as the valve, the fluid pressure so that the valve from the valve seat sealing surface lift, the media back to the valve back to the valve seat, and cut off the flow. Depending on the conditions of use, the flap may be of the all-metal structure or in the form of a rubber pad or rubber ring in the flap frame. Like the shut-off valve, the passage of the fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than the swivel check valve and the flow of the swivel check valve is limited Very few Check valve according to its structure and installation can be divided: First, the swing check valve: Swing check valve disc was disc-shaped, around the seat of the shaft for rotary motion, because the valve channel into Streamlined, flow resistance than the lift-type check valve is small, suitable for low flow and flow changes in the large diameter of the occasion, but not for pulsating flow, the sealing performance of less than lift. Swing check valve is divided into single, double and multi-type three, these three forms mainly by the valve caliber to the purpose, in order to prevent the media to stop the flow or back flow, weaken the hydraulic shock. Second, the lift check valve: valve flap along the valve body vertical center line sliding check valve, lift check valve can only be installed in the horizontal pipe, high pressure small diameter check valve on the valve can be used ball The The shape of the valve body of the lift check valve is the same as that of the globe valve (which can be used with the globe valve), so its fluid resistance coefficient is large. The structure and the valve is similar to the valve body and valve and the same valve. The upper part of the valve flap and the lower part of the valve cover are machined with a guide sleeve. The valve guide can be freely lifted in the valve guide. When the medium flows downstream, the valve flap is opened by the medium thrust. When the medium stops, Hanging down on the seat, from the media to prevent countercurrent effect. Straight-through lift check valve medium inlet and outlet channel direction and the direction of the valve seat channel vertical; vertical lift check valve, the media inlet and outlet channel direction and the same direction of the valve seat, the flow resistance is relatively straight through. Third, the disc check valve: valve flap around the valve seat rotation of the check valve. Disc-type check valve structure is simple, can only be installed in the horizontal pipe, the seal is poor.
Check valves are the basic components of fluid control engineering and are widely used in social production. Check valve by stopping the flow of fluid, play a control fluid medium direction, the role of protection of pipeline safety. Usually the check valve is automatically working, in a direction of the flow of media pressure, the valve flap open; when the media reverse flow, due to the pressure of the media and the role of self-weight valve, valve back seat, thus cutting off the fluid.
The performance of the check valve has a direct impact on the entire engineering system, it can be very good to prevent the impact of high pressure water pump impeller. If the pump outlet does not install the check valve, the high pressure water will reverse flow back to the pump, so that the pump impeller in the impact of high pressure water generated reverse, the impeller to withstand the impact of high pressure water load, and other parts will be loose or damaged When the pump is running again, it may cause the impeller to fly out and bring great safety risks.
The importance of the check valve can not be ignored, especially in the boiler hot water system and solar water heater system, if the hot water back to the pipeline, the PVC material will cause serious damage to the pipeline, and even endanger personal safety.